1. Technical Field
The present invention relates to a method of manufacturing a thin film transistor.
2. Related Art
When manufacturing a thin film transistor (TFT) serving as a switching element used in an electro-optical device, such as a liquid crystal device, a photolithography method has been used in a process of forming an electrode, a wiring line, or the like. The photolithography method forms a conductive film using existing film forming methods known as a sputtering method, a plating method, or a CVD method, applies a photosensitive material called a resist on a substrate, develops the resist by radiating light thereon, etches the conductive film according to a resist pattern, and forms a wiring line pattern or an electrode of a functional thin film. In the case in which the functional thin film is formed using the photolithography method, when a film forming process and an etching process are performed, large equipment such as a vacuum device and a complicated process are required, and a usage effectiveness of the material is only several percent, and thus most of the material is wasted, which causes a manufacturing cost to increase and causes productivity to deteriorate.
Accordingly, one method has been suggested in which an electrode pattern or a wiring line pattern (thin film pattern) is formed on a substrate using a droplet ejection method (a so-called inkjet method) to eject a droplet of a liquid material from a droplet ejection head (for example, Japanese Unexamined Patent Application Publication No. 2003-317945). In this method, ink for a thin film pattern, which is functional liquid obtained by dispersing conductive fine particles of metal fine particles or precursors thereof, is coated directly on a substrate, and is converted into a thin conductive film pattern by performing a thermal process or laser irradiation. According to this method, since a conventional complicated film forming process, a photolithography process, and an etching process become unnecessary, the process becomes simple, the amount of utilization of a raw material is small, and productivity increases.
According to the method disclosed in Japanese Unexamined Patent Application Publication No. 2003-317945, a bank is formed corresponding to a desired thin film pattern, and functional liquid is ejected between the banks and is then dried or baked, thereby obtaining a thin film pattern. However, according to this method, since the main object is to form a single thin film pattern, a technology for forming a laminated film obtained by laminating two films using functional liquid or a connection film obtained by connecting the two films is not disclosed.
As disclosed in Japanese Unexamined Patent Application Publication No. 2003-317945, when the second functional film including the side surface of the first functional film is laminated on the first functional film or connected to the first functional film after forming the first functional film using the bank, it is necessary that the bank be formed again and modified using the photolithography method. As such, when the bank is formed again, there occurs a problem in precision when the photolithography method is carried out, or there is a problem in that the number of processes increases, which results in an increase in costs. In addition, when there is a step difference that has a thickness of more than a thickness of a film formed on a base of an electrode or wiring line formed using the functional liquid, a thickness difference after forming a film significantly increases due to characteristics of a thin forming method using the functional liquid, thereby causing a short circuit of a film.